The fact that independent devices of various fixed and/or portable types are used for emergency lighting is currently known. A requirement for the existence of independent emergency lighting is made by the legal regulations applying to places of work, storage of hazardous materials, units for the production and transforming of electrical power, underground or enclosed car parks, premises used for accommodation and public spectacles or meetings, schools, hospitals, etc. some devices can be located in rooms separate from those in which the lamps are mounted, others are installed in an appropriate position close to the ceiling lights whose operation they are designed to ensure. Others again may be placed within the ceiling lights themselves and provide protection against interruptions in the main power supply. All devices have the common feature that their emergency operation is activated as soon as there is a lack of main power, whether they are mounted with lamps for continuous lighting or with lamps for non-continuous and only emergency lighting. Under emergency conditions electrical power is provided by appropriate batteries, which in general are rechargeable.
The problems of knowing the state of charge of the batteries and the reliability of the circuits at all times and of estimating the effectiveness of such equipment when needed have not been solved in the prior art. Periodical inspection to check condition involves operations which are not always easy and are selective and in any event burdensome to the user who very often has to check the operation of a number of separate independent units at different locations within a variety of environments.